System and method for biphasic transdermal iontophoretic delivery of therapeutic agents

ABSTRACT

Various embodiments provide methods and systems for the biphasic iontophoretic transdermal delivery of therapeutic agents. An embodiment of a method for such delivery comprises positioning at least one electrode assembly in electrical communication with a patient&#39;s skin. The assembly includes a solution comprising a therapeutic agent which passively diffuses into the skin. A dose of agent is delivered from the assembly into the skin during a first period using a first current having a characteristic e.g., polarity and magnitude, to repel the agent out of the assembly. During a second period, a second current having a characteristic to attract the agent is used to retain the agent in the assembly such that delivery of agent into skin is minimized. A dose of agent may be delivered on demand by an input from the patient. Embodiments may be used for delivery of agents which cause adverse effects from unwanted passive diffusion.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/755,840, filed Jun. 30, 2015, which is a divisional of U.S. patent application Ser. No. 13/430,662, filed Mar. 26, 2012 (now U.S. Pat. No. 9,095,503), which application claims the benefit of Provisional U.S. Patent Application Ser. No. 61/465,896, entitled “Biphasic Transdermal Iontophoretic System For The Transdermal Delivery Of Therapeutic Agents”, filed Mar. 24, 2011; and Provisional U.S. Patent Application Ser. No. 61/518,486, entitled “Biphasic Transdermal Iontophoretic System For The Transdermal Delivery Of Therapeutic Agents For The Control Of Addictive Cravings”, filed May 6, 2011. Said Ser. No. 14/755,840 is also a continuation-in-part of U.S. patent application Ser. No. 12/537,243, entitled “Iontophoretic System For Transdermal Delivery Of Active Agents For Therapeutic And Medicinal Purposes”, filed Aug. 6, 2009 (now U.S. Pat. No. 8,190,252), which claims the benefit of Provisional U.S. Patent Application No. 61/152,251 entitled “Kit, System and Method for Transdermal Iontophoretic Delivery of Therapeutic Agents”, filed Feb. 12, 2009. All of the above-identified applications are fully incorporated by reference herein for all purposes.

FIELD OF THE INVENTION

Embodiments described herein relate to assemblies and methods for transdermal drug delivery. More specifically, embodiments described herein relate to assemblies and methods for iontophoretic transdermal delivery of drugs and other therapeutic agents.

BACKGROUND

Chronic pain is a debilitating disease affecting millions of Americans. It destroys quality of life, results in significant number of lost work days and costs billions of dollars each year. Current forms of pain management include IV and oral delivery of various opioids and other pain medication. However, both IV and oral forms of drug delivery have a number of limitations. Both, in particular oral forms, can be ineffective for the treatment of chronic breakthrough pain. Breakthrough pain is pain that comes on suddenly for short periods of time and is not alleviated by the patients' normal pain suppression management. It is common in cancer patients who commonly have a background level of pain controlled by medications, but the pain periodically “breaks through” the medication. The characteristics of breakthrough cancer pain vary from person to person

Also both oral and IV forms of opioids and other pain medication are susceptible to the development of patient addiction due to excessive self medication. Further, both put the patient at risk of overdose and underdose due to unpredictable pharmaco-kinetics. The former resulting in a number of complications including addiction, depressed respiration, irregular heart rate and even death. The latter includes continued patient exposure to chronic pain. Also, oral delivery can have poor absorption particularly in the presence of other medications or food resulting in a delayed or uneven analgesic/therapeutic effect which in turn causes the patient to take more, thus increasing the chances of addition. Also, a number of oral analgesics, NSAIDS (non-steroidal anti-inflammatory drugs) for example, cause intestinal bleeding and various GI problems, such as cramping, etc. Intravenous limitations include the requirement to mix and store the medication in liquid form as well as the use of sterile techniques in administration. Also, IV administration can include several risk factors including anaphylaxis and cardiovascular complications. Thus, there is a need for improved methods of drug delivery for pain management.

Transdermal iontophoresis is a non-invasive method of propelling high concentrations of a drug or other therapeutic agent through the skin of a human or other animal by repulsive electromotive force using a small electrical charge. The electrical charge repels ionized (i.e., charged) forms of the drug or other therapeutic agent. Using such an approach, doses of pain medication can be delivered to the patient using a skin contacting patch containing pain medication that has been dissolved in a solution disposed within the patch. The application of a current causes the dissolved medication to be propelled from the solution through a contacting layer of the patient and into the skin. However, over-administration/overdose remains a problem for such devices due to the fact that the pain medication continues to passively diffuse from the patch reservoir into the patient even when iontophoretic current is off due to concentration gradients between the patch and the skin (under the principles of Fickian diffusion). Also, there is nothing to stop the patient from overdosing themselves by reactivating the device or even leaving the current on continuously to give themselves repetitive or even continuous doses. Improved systems and methods are needed for preventing over-administration of drugs due to passive diffusion as well as excessive administration by the patient.

BRIEF SUMMARY

Embodiments of the invention provide methods and assemblies for the transdermal delivery of drugs and other therapeutic agents to humans, mammals and other animals. Many embodiments provide a biphasic transdermal iontophoretic system having a delivery current to deliver doses of a therapeutic agent over a delivery period and a holding current to substantially halt or reduce the delivery of agent during a non-delivery period. Such embodiments can be configured to allow for repetitive cycles of delivery and non-delivery of drugs and other therapeutic agents to treat various conditions. Further, various embodiments provide systems and methods allowing for on-demand initiation of a delivery period (e.g., by the patient, caregiver or other person) to allow for treatment of various acute conditions such as pain, nausea (e.g., chemotherapy induced), migraine headache and other conditions. Such systems and methods can be configured for use in the delivery of various analgesic agents including opioids such as fentanyl and its derivatives and analogues. Other embodiments can be configured for use in the delivery of various antiemetics such as dolasetron (and other 5-HT3 receptor antagonists), domperidon (and other dopamine antagonists) and promethazinen (and other antihistamines).

Still other embodiments of systems and methods of the invention provide for controlled initiation of a delivery period and/or cycles of delivery and non-delivery by a controller such as a microprocessor or other controller known in the art (e.g., an analogue controller). Such embodiments can be configured for the cyclical delivery of a variety of therapeutic agents including, for example, parathyroid hormones and like compounds for the treatment of osteoporosis and various chemotherapeutic agents for the treatment of cancer. Further, such embodiments are particularly useful for the delivery of therapeutic agents where the time course of delivery of the agent needs to be controlled to produce a desired therapeutic effect and/or to minimize adverse effects to the patient. Such controlled initiation (either of a delivery period or cycle of delivery and non delivery periods) can be incorporated into a delivery regimen which can be programmed into the controller either directly, wirelessly or by means of a memory device operably coupled to the controller. The system can be configured to allow the program to be selected by a doctor, pharmacist, or other medical care provider. The selection can be done directly by the medical care provider via an input device (e.g., touch screen) coupled to the controller or wirelessly using a wireless device such as a cell phone, tablet device or like device. In either case, lockout codes can be employed to prevent anyone but the medical care provider from entering or changing a particular delivery regimen.

One embodiment provides a method for the transdermal delivery of a therapeutic agent to a patient comprising positioning at least one electrode assembly in electrical communication with a patient e.g., with the patient's skin. The electrode assembly includes a skin contacting layer and a solution having a dissolved therapeutic agent having an electrical charge, wherein the dissolved agent passively diffuses into the skin without the application of an external force. A first dose of agent is delivered from the electrode assembly into the skin during a first period using a first current having a polarity and magnitude or other characteristic to repel the agent out of the assembly. During a second period, a second current having a polarity and magnitude or other characteristic to attract the agent is used to retain the agent in the assembly such that delivery of the agent into the skin during the period is minimized. Embodiments of this method are particularly useful for the delivery of various therapeutic agents, such as opioids where over-delivery of the therapeutic agent from passive diffusion may be harmful to the patient.

Further details of these and other embodiments and aspects of the invention are described more fully below, with reference to the attached drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing the three main layers of the skin, the epidermis, the dermis and subcutaneous tissue as well as the passageways into the skin.

FIG. 2 is a lateral view of an embodiment of a system for the transdermal iontophoretic delivery of various therapeutic agents using delivery and lateral electrodes.

FIG. 3a is a schematic side view showing placement of an embodiment of a transdermal iontophoretic patch device on the surface of the skin, wherein the device comprises an active electrode assembly and a return electrode assembly.

FIG. 3b is a schematic side view showing placement of an embodiment of transdermal iontophoretic patch device on the surface of the skin, wherein the device comprises two active electrode assemblies.

FIGS. 4a and 4b are side and top views showing an embodiment of a skin patch including an active electrode and lateral electrodes.

FIG. 5a is a top down view showing an embodiment of an on demand user-activated transdermal delivery system including a patch assembly.

FIGS. 5b, 5c and 5d are time sequence graphs illustrating an embodiment of a patient controlled or other “on-demand” biphasic transdermal iontophoretic delivery system having a delivery current and a holding current so as to cycle between delivery periods and non delivery periods of a drug or other therapeutic agent. FIG. 5b shows an activation signal for initiating a drug delivery cycle, the signal generated by a patient activated device or other signal generation means; FIG. 5c shows an embodiment of a current waveform initiated by the activation signal the waveform having a delivery current and holding current; FIG. 5d shows an embodiment of a drug delivery profile corresponding to the periods of delivery current and holding current.

FIGS. 6a and 6b are perspective views showing an embodiment of a system/patch assembly for iontophoretic transdermal delivery of a therapeutic agent including a patch and an electronics assembly, FIG. 6a shows a top view, FIG. 6b shows a bottom view. FIG. 6c is a block diagram of an embodiment of the electronics assembly including a controller, current source and current switching device.

FIG. 7a is a perspective view showing placement of the embodiment of FIGS. 6a and 6b on an example site on the skin of a user.

FIG. 7b is a lateral view showing an embodiment of a patch assembly having a curved contour positioned at a tissue site having a curved contour.

FIGS. 8a through 8f illustrate various waveforms or current output variations that can be used to promote various characteristics of embodiments of the transdermal iontophoretic delivery system.

FIG. 9 is a block diagram of a transfer function used to model an embodiment of the transdermal iontophoretic delivery system used in the example.

FIGS. 10a and 10b are plots of delivered therapeutic agent versus time. FIG. 10a shows the cumulative input vs. the estimated system response based on an optimum cross-correlation FIR filter response of the measured system response; FIG. 10b plot shows the density input vs. the estimated system response based on an optimum cross-correlation FIR filter response of the measured system response.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments described herein provide a device, system and method for the transdermal iontophoretic delivery of various drugs and other therapeutic agents. Many embodiments provide devices, systems and methods for the biphasic transdermal iontophoretic delivery of various therapeutic agents such as opioids and antiemetics. As used herein, the term transdermal delivery refers to the delivery of a compound, such as a drug or other therapeutic agent, through one or more layers of the skin (e.g., epidermis, dermis, etc.). Referring now to FIG. 1, the layers of the skin include the epidermis EP, dermis D and subdermis SD. The upper most layer of the epidermis includes the stratum corneum SC, a dead layer of skin (having a thickness of about 10 to 40 μm) and the viable epidermis EP. Transdermal delivery can proceed by one of the three passage ways into the skin, via 1, the sweat pores SP, 2, the hair follicles HF or via permeation 3 through the epidermis EP (starting at the stratum corneum) and the dermis.

Iontophoresis is a non-invasive method of propelling high concentrations of a charged substance, known as the active agent, transdermally by repulsive electromotive force using a small electrical charge. The active agent can include a drug or other therapeutic agent. The charge is applied by an electrical power source to an active electrode assembly placed on the skin which contains a similarly charged active agent and a solvent in which it is dissolved. Current flows from the electrode assembly through the skin and then returns by means of a return or counter electrode assembly also placed on the skin. A positively charged electrode assembly, termed the anode will repel a positively charged active agent, or anion, into the skin, while a negatively charged electrode assembly, termed the cathode, will repel a negatively charged active agent, known as a cation, into the skin.

Referring now to FIGS. 2-4 b, an embodiment of a system 5 for the transdermal iontophoretic delivery of a therapeutic agent 51 to a tissue site TS (such as the arm A) also referred to as a delivery site TS, on the skin S of patient, comprises at least two electrode assemblies 14 including an active electrode assembly 20 and a return electrode assembly 30 and a power supply 100. Active electrode assembly 20 is used to deliver the therapeutic agent through skin S via current delivered to the skin from power supply 100. Return electrode assembly 30 provides a return path for current (e.g., current 60) to power supply 100. Collectively, the active and return electrode assemblies 20 and 30 comprise a transdermal iontophoretic delivery device 10 also described herein as patch device 10. In embodiments using an alternating current, both electrode assemblies 14 can be configured as active and return electrode assemblies 20 and 30 depending on the direction of current flow. In some cases for sake of brevity, electrode assembly 14, active electrode assembly 20 and/or return electrode assembly 30 will sometimes be referred to as electrode 14, active electrode 20 and return electrode 30 respectively.

In many embodiments, the electrode assemblies 14 (e.g., active and return assemblies 20 and 30) comprise or are otherwise disposed on one or more patches 15 configured to be applied to the skin surface. Patches 15 are desirably conformable to a contour CR of a skin surface S and can be fabricated from layers of elastomeric or other flexible polymer material. In some embodiments, two or more electrodes assemblies 14 including active and return electrode assemblies 20 and 30 can be placed on a single patch 15. In other embodiments, system 5 can include separate patches 15 for electrode assemblies 14, for example, a first patch 15′ for the active electrode assembly 20 and a second patch 15″ for the return electrode assembly 30. In other embodiments, three or more patches 15 can be used so as to have either multiple active electrode assemblies 20 or return electrode assemblies 30 or both. For example, in one embodiment system 5 can comprise three patches 15; including two patches containing active electrode assemblies 20 and a third patch 15 containing a return electrode assembly 30. Other combinations of multiple patches and electrode assemblies are also contemplated, e.g., four patches, two for active electrode assemblies 20 and two for return electrode assemblies 30.

In many embodiments, active electrode assembly 20 can comprise a reservoir 21 for the therapeutic agent, a tissue contacting porous portion 24 in fluidic communication with the reservoir, an adhesive portion 25 for adhering the assembly to the skin, and an electrical connector 26 for coupling the electrode assembly 20 to an electrical power supply 100 as is shown in the embodiment of FIG. 2. Reservoir 21 can be sized for the particular dose of therapeutic agent to be delivered. In various embodiments, the power supply 100 can include various features to facilitate use by medical personnel both in a hospital setting and in the field. For example, the power supply can include or be configured to be coupled to a bar code reader (not shown) for reading bar codes positioned on one or more of electrode assemblies 14, patches 15 or power supply 100.

Tissue contacting portion 24 is also electrically conductive (herein conductive) so as to function as an active electrode 20 and/or return electrode 30. This can be achieved by fabricating tissue contacting portion 24 from conductive porous materials (e.g., conductive carbon or other conductive fibers) and/or by having it become wetted with a conductive solution 54 (the conductivity being due to therapeutic agent 51 or various electrolytes added to the solution). Connector 26 can extend into or otherwise make electrical contact with tissue contacting portion 24 so to be electrically coupled to portion 24. In some embodiments, connector 26 can be coupled to a conductive element 28 positioned within the electrode assembly 14 and coupled to conductive porous portion 24. One or more of conductive element 28, conductive layer 34 (described below) as well as lateral electrodes 40 (also described below) can comprise various conductive materials including stainless steel, carbon, silver chloride (AgCl) or other conductive materials known in the art.

Typically, adhesive portion 25 will surround the perimeter 24 p of porous portion 24 as is shown in the embodiment of FIGS. 4a and 4b , though other arrangements are also contemplated. In various embodiments, porous portion 24 can comprise a porous layer 24 that in turn comprises various porous materials including polymers foams, membranes or weaves of polymer fibers known in the art including polyesters, PETs and like materials. Adhesive portion 25 may be attached to porous layer 24 and include various releasable adhesives known in the art. The adhesive portion 25 can comprise an adhesive layer 25 a, such as one or more releasable adhesives attached to a substrate layer 25 s, which can comprise various hydrogels, polyurethanes, silicones or like polymeric materials. The size and configuration of adhesive portion 25 can be adapted for the particular skin location (e.g., arm vs. leg, amount of hair, etc.) and type of skin (e.g., pediatric vs. geriatric etc., amount of hair, etc.).

Typically, the therapeutic agent 51 will be dissolved in a therapeutic agent solution 54, also described as therapeutic agent composition 54 which is used to fill reservoir 21. In addition to therapeutic agent 51, solution 54 can include one or more pharmaceutical excipients 52 such as preservatives (e.g., citric acid). The viscosity of the solution 54 can be adjusted to have the solution readily wick from reservoir 21 into porous layer 24. Solution 54 can be preloaded into the reservoir 21 at the factory or can be added by medical personnel prior to use through means of a port 22, such as a self-sealing port (allowing injection of liquid through the port) which is coupled to reservoir 21 via means of a channel 27 as is shown in the embodiment of FIG. 3b . Suitable therapeutic agents 51 can include, without limitation, ferric pyrophosphate or other iron containing compound for the treatment of iron deficient anemia, insulin or various glucagon like peptides for treatment of diabetes or other blood sugar regulation disorder, fentanyl or other opioid compound for pain management and various chemotherapeutic agents for the treatment of cancer.

The return electrode assembly 30 comprises a tissue contacting conductive layer 34, an adhesive layer 35 and a connector 26 for coupling the electrode assembly to the electrical power source. In many embodiments, the return electrode assembly 30 can have substantially the same elemental configuration as active electrode assembly 20 (e.g., a reservoir 21, conductive tissue contacting layer 24) so as to function as an active electrode assembly as is shown in the embodiment of FIG. 3 b.

In many embodiments, patch 15 also includes one or more pair of electrodes known as lateral electrodes 40. Lateral electrodes 40 are desirably placed on either side of porous portion 24 at a selectable distance from the perimeter 24 p of porous portion 24 as is shown in the embodiments of FIGS. 3a-3b and 4a-4b . Lateral electrodes 40 can comprise various conductive materials including metals, graphite, silver chloride and other like materials. In various embodiments, all or a portion of lateral electrode 40 can include an insulative coating so as to be a capacitively coupled electrode that delivers current to the skin via capacitive coupling. Lateral electrodes 40 are also desirably electrically isolated from electrodes 20 and 30 and will typically include their own wave form generator circuits.

The lateral electrodes 40 are desirably arranged with respect to porous portion 24 such that they result in a conductive pathway 104 which goes through the skin S underlying portion 24 and is substantially parallel to the skin. Embodiments of patch 15 that employ lateral electrodes 40 with delivery electrodes 20, allow for the flow of two currents, a first current 60 and a second current 70. First current, 60 flows between electrodes 20 and 30 and serves to provide an electromotive force which acts to drive the therapeutic agent 51 into and across the layers of the skin S. The second current 70, known as sieving current 70, provides an electromotive force that acts on the therapeutic agent 51 in a direction parallel to the skin S so as to cause oscillation of therapeutic agent 51 in a direction parallel to skin S. This oscillation acts to sieve the therapeutic agent through pathways of lesser or least diffusional resistance in the skin. For embodiments where second patch 15″ contains lateral electrodes 40 and is used to deliver therapeutic agent, a third current 70′ can be delivered from lateral electrodes on the second patch 15″ to also create an electromotive driving force to oscillate the therapeutic agent substantially parallel to the skin surface underneath the second patch 15″. Further description on the arrangement and use of lateral electrodes 40 including their use in generating a sieving current is found in U.S. patent application Ser. No. 12/658,637, filed Feb. 10, 2010 which is incorporated by reference herein in its entirety.

Referring now to FIGS. 5a-5d , various embodiments of the invention for use in on demand transdermal delivery of a therapeutic agent will now be described. Such embodiments include systems 5′ and methods for on demand delivery of therapeutic agents 51. As used herein, the term “on demand”; refers to the ability of the patient or other person (e.g., a medical care provider) to initiate the delivery of therapeutic agent. This includes the initiation of a therapeutic agent delivery period and/or cycle of therapeutic agent delivery periods described below. The initiation of any of these can be a signal/input from a patient activation device such as a push button device and/or a signal received from a wireless device such as cell phone or other RF-enabled device. Such “on demand” embodiments provide for one or more of the following: i) the ability for the patient, other user or a controller/machine to initiate the delivery of therapeutic agent 51 to the patient; and ii) the ability to stop or otherwise limit the passive diffusion of therapeutic agent 51 during periods of time when an iontophoretic current is not supplied to patch assembly 15 cp. In many embodiments, on demand transdermal delivery can be implemented by use of a biphasic transdermal iontophoretic delivery system 5″ (biphasic transdermal iontophoretic delivery is defined and further described below). Such embodiments are particularly useful for the delivery of therapeutic agents 51 p (herein after pain medication 51 p) for the treatment of pain (e.g., pain reduction), such as an opioid-based pain medication (e.g., fentanyl and its analogues). However, it should be appreciated that embodiments of such a system 5″ can be used for the delivery of any therapeutic agent 51 described herein or known in the art for the treatment of any number of conditions.

Referring now to FIG. 5a an embodiment of an “on demand” transdermal delivery system 5′ will now be described. The system may configured for on demand delivery of therapeutic agent 51 by the patient and/or a medical care provider. System5′ may also be configured as a biphasic transdermal iontophoretic delivery system 5″ described herein, for example, through the use of a control program 93 p described below. The system 5′ includes a patch assembly 15 cp including a patch 15, electrodes 14, therapeutic agent reservoir 21 and electronic module or section 90 including a user activated device 91 (also referred to as activation device 91) for allowing the patient or other user to initiate delivery of therapeutic agent 51. Electrodes 14 and will typically include a delivery or active electrode 20 and a return electrode 30 as described herein. Active electrode 20 is configured to be in fluidic communication with a therapeutic agent reservoir 21 for storing a supply of therapeutic agent 51. As described herein, in many embodiments, therapeutic agent 51 will be dissolved in a solution 54 (contained in reservoir 21) so as to be in ionic form. According to one or more embodiments, solution 54 containing therapeutic agent 51 can be loaded into reservoir 21 at the factory and/or at the pharmacy by a pharmacist before pickup by the patient. According to other embodiments, therapeutic agent 51 is stored in reservoir21 in solid form and liquid comprising solution 54 is added to the reservoir by the user or medical care provider immediately prior to use.

In various embodiments, patch 15 can have a substantial oval shape 15 o including, for example, peanut or cassini-shaped ovals 15 oc having side portions 15 s and a tapered center portion 15 c as is shown in the embodiment of FIG. 5a . Electrodes 14 including active electrode 20 and return electrode 30 can be positioned in side portions 15 s and an electronics module 90 positioned in the center portion 15 c. Desirably, electrodes 20 and 30 are positioned on opposite side portions 15 s as is shown in the embodiment of FIG. 5a ; however other configurations are also contemplates such as the placement of electrodes 20 and 30 in each side portion 15 s. Electronics module 90 can include a controller 93 which may correspond to controller 530 (shown in FIG. 6a ) and a power source 97 which may correspond to power source 570 (shown in FIG. 6b ) and can include an electrochemical storage battery and circuitry for converting a DC (direct current) signal from the battery(s) into an AC (alternating current) signal. The electronics module 90 includes a user activation device 91 such as a push-button or switch for initiating a drug delivery cycle to deliver a dose of an opioid or other therapeutic agent 51 (e.g., an antiemetics). Other electromechanical activation devices 91 known in the art are also contemplated. Typically, activation device 91 is coupled to controller 93 (or other controller) so that signals 91 s generated by device 91 provide an input to the controller for initiating a function such as initiation of a delivery period and/or delivery cycle of therapeutic agent 51. However, in additional or alternative embodiments, activation device 91 may comprise an externally connected device such as a push-button device that is electrically connected to module 90 (e.g., by a wire) and positioned and configured for easy access by the patient (e.g., a device that is attached to the patient belt or may lie by the patients bed side). In still other embodiments, activation device 91 may comprise a wireless device, such as a cell phone, pda or RF-enabled communication device that can be carried, worn or placed in close proximity to the patient. For such wireless embodiments of device 91, device 91 and/or controller 93 may include various passwords or other codes to prevent accidental and/or other unauthorized use.

Referring now to FIGS. 5b-5d , embodiments of a method for “on demand” drug delivery using a biphasic transdermal iontophoretic delivery system 5″ will now be described. Embodiments of this method are applicable with various embodiments of the patch and electrode assemblies described herein such as patch assembly 15 cp and 500. “Biphasic transdermal iontophoretic delivery” refers to the use of a transdermal iontophoretic delivery system having a first and second phase of drug delivery. In some embodiments, the first and second phase of drug delivery may correspond to a delivery period and a non-delivery period. The delivery period in turn may correspond to a period of active transport of the therapeutic agent (e.g., using a drive current) and the non-delivery period to a period of active inhibition of such transport (e.g., using a holding current). As shown in FIGS. 5b-5d , before the initiation of a delivery cycle (e.g., by the patient, or other user) no or minimal agent is delivered as the agent is held within reservoir 21 by a holding current 320 described below. When the patient presses activation device 91 this generates a signal 300 which is fed into the controller 93. The controller 93 can include a control program or other logic 93 p for starting a drug delivery period 340 upon receiving the signal 300. The control program 93 p then initiates the beginning of a drug delivery period 340 by the flow of a first current known as a drug delivery current 310 (also referred to herein as a drive current 310) which has a polarity and magnitude or other characteristic configured to repel therapeutic agent 51 from the reservoir 21 and into the skin (the polarity being the same in sign (i.e., positive or negative) to the charge to that of the ionic form of therapeutic agent 51). The other characteristics of current 310 can include, without limitation one or more of the voltage, frequency/period or shape of the waveform of current 310 (these characteristics can also be used for adjustment of holding current 320 to perform its function).

Controller 93 keeps the delivery current 310 on for the delivery period 340 to deliver a selected dose of the therapeutic agent 51 into the skin as shown by the delivery curve 350 in FIG. 5d (the delivery period and delivery current can be stored in controller 93 and/or determined by program 93 p for example using the transfer function and other modeling methods described in the appended example). At the end of the delivery period 340, the controller stops the delivery current 310 and starts a non-delivery period 330 (also known as refractory period 330) by generating a holding current 320. Holding current 320 has a polarity and magnitude or other characteristic configured to retain agent 51 within reservoir 21 by the force of electrostatic attraction (e.g., the polarity of the holding current 320 has the opposite sign as the charge of the ionic form of the therapeutic agent) so as to prevent or minimize passive diffusion of the therapeutic agent from the patch into the skin. Such minimal diffusion is shown in the non-delivery curve 360 in FIG. 5d . Such passive diffusion would otherwise occur without the presence of attractive force from the holding current 320. In particular embodiments, one or more characteristics of holding current 320 can be adjusted relative to the concentration of the therapeutic agent 51 within solution 54 and/or other property of solution 54 so as to assure that the holding current is sufficient to retain agent 51 within reservoir 21. For example, the magnitude of the current 320 can be proportionally or otherwise adjusted (e.g., geometrically) relative to the concentration of therapeutic agent 51 within solution 54. The adjustment can be done at the factory, by the medical caregiver or via software within controller 93. The adjustments can also be done dynamically over the course of a delivery cycle to account for changes in the changes of the concentration of agent 51 within solution 54. In particular embodiments, a sensor may be employed to measure the concentration of agent 51 within solution 54 within output of the sensor being fed as an input to controller 93. In related embodiments similar adjustments can be in the characteristics of current 310 relative to the concentration of agent 51 in solution 54 or other property of solution 54 so as to assure that sufficient agent 51 is delivered out of reservoir 21 and into the patient's skin.

Also, during non-delivery period 330, the controller locks out or otherwise prevents the start of another delivery period so as to prevent the patient (or other person) from repetitively dosing themselves and thus overdosing themselves. After the lockout period, the controller then allows the start of another delivery cycle. The controller can also be programmed or otherwise configured to only allow a maximum number of administered doses of agent 51 over a selected period of time, for example, 12, 24 hours etc. In particular embodiments for the delivery of opioid-based therapeutic agents 51 p, such as fentanyl and its analogues, the maximum number of doses can correspond to 24, 40, 48, 60, 80, 98 or 100 doses. Desirably, the maximum number of doses is configured to keep the concentration (e.g., plasma concentration) of therapeutic agent within a therapeutic index (known in the art) and prevent the dose from exceeding a maximum tolerated dose such as that which would cause or begin to cause respiratory depression, low blood pressure, slowed heart rate and/or other adverse physiologic affects. Similarly, the maximum number of delivered doses and/or lockout period can be selected to keep the rate of delivery of therapeutic agent 51 to the patient below that which would cause such adverse affects. The maximum number of dose and lockout period can be determined based on one or more parameters including without limitation, the therapeutic agent, the patient's age and weight, their condition and other therapeutic agents they are receiving (currently, previously or in the future).

Referring now to FIGS. 6a, 6b, 6c, 7a and 7b , in various embodiments, a system 500 for iontophoretic transdermal delivery of various pain medication 51 p and/or other therapeutic agents can comprise a skin conformable patch 505 and an electronics assembly 550. System 500 (also described herein as patch assembly 500) can be configured as an “on demand” transdermal delivery system 5′ and/or biphasic transdermal iontophoretic delivery system 5″ as described herein. Patch 505 includes first and second electrode assemblies 510 and 512 which can correspond to one or more embodiments of electrode assemblies described herein. The materials used to fabricate the electrode portions of the assemblies can include various corrosion resistant materials such as graphite further described in U.S. patent application Ser. Nos. 12/824,146 and 12/824,147 (both filed Jun. 10, 2010) which are fully incorporated by reference herein for all purposes. Also, one or both of electrode assemblies 510 and 512 can include a pair 520 of tissue contacting ring shaped electrodes 521 and 522 concentrically spaced or otherwise arranged to reduce edge effects as is further described in U.S. patent application Ser. No. 12/832,011 (filed Jul. 7, 2010) which is fully incorporated by reference herein for all purposes.

Electronics assembly 550 typically includes a housing 560 which engages patch 505 so as to form patch assembly 500. Housing 560 includes a bottom and top surface 561 and 562 respectively, with the bottom surface 561 typically being the area of contact for engaging patch 505, though other arrangements are also contemplated. In particular embodiments, the housing 560 can be configured to be detachably coupled to patch 505 via one or more detachment elements 600.

Housing 560 can have a variety of shapes. In many embodiments, it can include a shaped contour 563 such as a curved shaped contour 564 (which can be for one or both of bottom surface 561 and top surface 562) that is configured to correspond to the contour C of the skin surface SS at the target tissue site TS where patch assembly 500 is placed such as the contour of the patient's arm, leg or abdomen (e.g., on the front or side of the stomach including below the waist line so as to not be visible). Contours 563 and 564 may: i) correspond to a standard contour for a particular target site TS; ii) may come in different sizes and shapes for different target tissue sites and sizes of patients; or iii) may be custom shaped for the particular patient and target tissue site. Also, the housing 560 can be conformable so as to at least partially conform to the contour C of the skin surface SS at the target tissue site TS where the patch 505 and housing 560 are placed (both when the patient is still and when they are moving resulting in bending movement and other deformation of the skin such that the skin surface contour is a flexing contour). Accordingly, in various embodiments, all or a portion of housing 560 can comprise various flexible polymers known in the art such as various elastomeric polymers, e.g., silicone and polyurethane. Other flexible polymers are also contemplated. The flexibility/conformability of the housing can also be configured to vary over the length of the housing to meet the needs of the particular target tissue site TS. For example, the housing 560 can be configured to have the greatest amount of flexibility at its center portions 560 c (which can be achieved in some embodiments by putting a crimp or articulated zone 560 a near the center of the housing). Also, the flexibility profile of the housing 560 can be matched or otherwise correlated to the shape and flexibility profile of the patch 505. For example, in particular embodiments, the flexibility/conformability of the housing can be configured for embodiments of the patch 505 having ring shaped electrodes 521 and 522. In these and related embodiments, housing 560 may have a structure which include areas 566 of greater flexibility (e.g., less stiffness) which may approximately align with ring shaped electrodes 521 and 522 (or others) such that the overall flexibility of the assembly 500 is not decreased over these areas. Areas 566 can have a shape which corresponds to the shape of electrodes 521 and 522 (or other shaped electrodes), though the size of the areas can be different from the size of the electrodes. Areas 566 can be achieved by decreasing the thickness of the housing in these areas and/or the use of more flexible materials. Other structures for housing 560 including shaped areas 566 are also contemplated, such as structures which have oval shapes areas 566 or even recessed areas 566.

Also in various embodiments, housing 560 cannot only be conformable, but also have a profile 565 shaped and sized such that the entire patch assembly 500 can be worn beneath the user's clothing and can bend and flex sufficiently so that: i) it is not readily detached by pressure or force from the user's clothing (due to movement of the clothes and/or skin), allowing the patch assembly 500 to stay on for extended periods when adhered to a tissue site underneath the user's clothes; and ii) is not readily visible beneath the user's clothes. In various embodiments, the profile 565 of the housing can have a contour 564 (of one or both of top and bottom surfaces 562 and 561) which corresponds to the contour C of the surface of the patient's arm, leg, abdomen or other target tissue site TS. Further, embodiments of the housing 560 can be sized, shaped and otherwise fabricated to bend and flex sufficiently to account for movement of the patient's skin when the patch assembly 500 is placed on the patient's abdomen, arm, leg and other target tissue sites. In this way, even when the patch assembly 500 is placed under clothes (or not), the assembly can remain sufficiently adhered/attached to the patient's skin for an extended period of time so as to allow a desired dose of the drug or other therapeutic agent 51 to be delivered. In various embodiments, the time period can be up to 24 hours, up to three days, up to a week with even longer periods contemplated. Specific combinations of a patch 505 and housing 560 can be configured for specific desired attachment periods using one or more factors described herein (e.g., flexibility surface area, etc.). For embodiments of the patch including elemental iron, such configurations can allow the patch to remain sufficiently adhered to the patient's skin for a sufficient time to deliver a therapeutic dose of elemental iron for the treatment of iron deficient anemia (e.g., 1 to 100 mg with specific embodiments of 20, 30 and 50 mg) at rates which facilitate uptake and utilization by the patient's iron metabolism. Similar configurations and methods can be employed for delivery of other drugs and therapeutic agents described herein (e.g. opioids such as fentanyl and its analogues and derivatives).

Further, one or more of the size and shape (e.g., shape of the housing bottom surface 561 such as oval, circular, dogbone etc.) and flexibility of the housing 560 can be selected relative to one or more of the size and shape (e.g., shape of patch surface 505 s) and flexibility of patch 505 such that when the patch assembly 500 is worn openly or beneath the patient's clothes, the applied amount of force from the housing 560 to the skin surface SS beneath the patch (due to movement of the patient's skin) or the clothing to the skin surface beneath the patch 505 (due to movement of the clothing or skin) is fairly uniform (e.g., there is a substantially uniform force distribution with minimal areas of force concentration). In use, these and related embodiments serve to minimize the amount of thermal, electrical or other injury to the skin from high current densities and/or hot spots from such force concentrations. Additionally for embodiments using delivery of therapeutic agent(s) 51 from embodiments of patch 505 having two more or electrode assemblies (e.g., assemblies 510 and 512) such configurations minimizing force concentrations(from skin movement etc) also serve to minimize any effect on the delivery of therapeutic agent from the first electrode relative to the second electrode (or others). In particular embodiments, this can serve to minimize any effect on the delivery rate or total delivered amount of therapeutic agent from the first electrode assembly 510 relative to the second electrode assembly 512 (or other electrode assemblies).

In particular embodiments, such results can be achieved by matching the flexibility of the housing 560 to the patch 505 (either approximately equivalent or a selected amount higher or lower, e.g., 5 to 50%) as well as configuring the surface area of the patch 505 to be large enough relative to the surface area of the housing 560 so as produce a snow-shoe like effect so as to evenly distribute any applied force to the housing from clothing or other applied force (such as that due to movement of the skin) over the entire surface area of the patch 505. Surface area ratios in the range of 1:1.5 to 1:10 (housing surface area to patch surface area) are contemplated, with specific embodiments of 1:2, 1:3, 1:5.

In still other embodiments, the housing 560 or patch 505 may include a pressures sensor 567, such as a solid state strain gauge which senses the amount of force applied by the user's clothes to the housing and/or patch. Input from the pressure sensor can then be used to modulate (either increase or decrease) current delivered to the patch relative to the applied force. The current can be modulated down to prevent the development of hot spots on the patch from excessive pressure or modulated up to account for any increase in the electrical impedance of the skin due to the applied pressure.

Assembly 550 will typically include a power source 570 (also referred to herein as current source 570) and a controller 530 (e.g., a microprocessor or like device) for controlling one or more aspects of the iontophoretic delivery of the agent to the skin. Controller 530 can also include an integrated or separate power controller 535 for controlling the delivery of current to the skin. One or both of the controllers 530 and 535 can be coupled to an H-bridge or other current switching/limiting device 540 for limiting or otherwise controlling the delivery of current to the skin. The housing will also typically include a cavity 580 for current source 570, such as a cylindrical shaped cavity which may be sized for standard size batteries such as AA or AAA batteries. Other shapes for cavity 580 are also contemplated.

In various embodiments, current source 570 can comprise one or more electrochemical batteries including an alkaline, lithium, lithium-ion and like chemistries. For ease of discussion, current source 570 will be referred to herein as battery 570 but other current sources are equally applicable. Battery 570 can also comprise a rechargeable battery known in the art. The battery 570 can have a selected capacity to deliver sufficient current/voltage to the skin for transdermal delivery of the therapeutic agent for periods ranging from 2 to 24 hours or even longer. Power source 570 may also correspond to alternating current power source. Accordingly, in embodiments including an electrochemical battery(s), power source 570 may include circuitry for converting a DC signal from the battery(s) into an AC signal. Other power/current sources 570 are also contemplated, such as various storage capacitors and piezo-electric based energy harvesting devices.

The patch 505 will typically include one or more conductive areas 506 for electrical coupling to conductive elements 591 on the electronics assembly 550. The conductive areas 506 can be coupled to conductive traces 590 placed on the patch surface 505 s or within the patch 505. The conductive elements on the electronics assembly 550 can be coupled to one or both of controller 530 and current source 570.

Detachment elements 600 can be spring loaded and can be configured to be engaged by the fingers of a user. In particular embodiments, detachment elements 600 may include or be mechanically coupled to one or more anchoring elements 601 such as a hook for anchoring into patch 505. The anchoring elements 601 may also comprise adhesive areas placed on the housing bottom surface 561 which engage the patch surface 505S.

In use, detachment elements 600 allow the user to attach and detach an electronics assembly 550 to a selected patch 505. This allows the electronics assembly 550 to be reused for multiple patches. In an exemplary embodiment of using system 500, the user can obtain a particular patch 505, scan information about the patch using a bar code reader (or other indicia reading means) described below and then attach the patch 505 to the assembly 550. When the user is done using the patch (e.g., such as when the desired amount of drug has been delivered) the user then detaches assembly 550 from the patch 505 discarding patch 505. In particular embodiments, assembly 550 can include programming which provides a signal such as beep or other alarm indicating to the user when to remove the patch 505. As an alternative, the patch surface 505 s can include an indicator portion 507 which changes color or otherwise provides visible indicia 508 to the user when the required amount of agent has been delivered to the skin. In one embodiment, the indicia 508 can comprise a symbol or marking 509 that becomes visible when the amount of therapeutic agent 51 has been delivered. Visibility of the marking can be due to depletion of therapeutic agent 51 within patch 505 and/or a chemical or electrochemical reaction within or on the patch.

In particular embodiments, the electronics assembly 550 can also include a bar code reader for reading a bar code printed on patch 505 for ascertaining various information about the patch 505 including for example, the type and amount of therapeutic agent 51 contained in the patch, a desired delivery regimen, lot numbers (of the patch 505 and the therapeutic agent 51) shelf life, expiration date and related information. In an additional or alternative embodiment, patch 505 may contain a memory device (e.g. an EEPROM and the like) 506 which contains similar information and is readable by electronics assembly 550 (e.g., by controller 530). Assembly 550 may also contain a memory device 556 for storing information (described above) which may be coupled to microcontroller 530. The information contained in memory device 556 (e.g., type, dose and lot number of therapeutic agent 51) can be entered at the factory and/or by the doctor or pharmacist. Also information entry can be done directly or over a network such as the internet or cellular phone network or other like network. Other indicia reading means, for reading/detecting other indicia of information about patch 505 are also contemplated. Such indicia reading means can include, without limitation, use of various RFID chips known in the art.

System 500 including patch 505 and assembly 550, can be sized and shaped to be placed in any number of locations on the patient's skin including the arm, leg or abdomen, back or other location. The particular material properties of the patch 505 and housing 560 (e.g., thickness, modulus of elasticity, bendability, etc.) can also be so selected to allow placement at the desired location. For example, more flexible material properties can be selected for placement of the system 500 over skin areas with greater amounts of bending by the user, such as the stomach. Also, patch 505 and assembly 550 can be packaged together, for example, as a kit 500 k (which can include instructions for use) wherein the assembly 550 is matched to patch 505 in terms of size, current source, programming mechanical properties etc. Further, a given assembly 550 can be calibrated for such a group of patches 505 or patches 505 from a particular lot number. In such embodiments, multiple patches 505 can be included with a particular assembly 550. In use, this allows the patient to obtain a complete supply of patches to meet the delivery requirements for a particular therapeutic agent 51 over a period of days, weeks, or months. Further, the assembly 550 can be programmed such that when the patient is near the end of his or supply of patches 505, that the assembly will give the patient a message to purchase more patches. In related embodiments, the assembly 550 can be configured to interface with the Internet and/or a mobile communication device such as cell phone, to send a message to the patient's pharmacy and/or doctor to do one or more of the following: i) renew the patient's prescription for a particular therapeutic agent patch 505; ii) have an order for a supply of the therapeutic agent patch 505 ready for the patient's pick up at his or her drug store; and/or iii) ship an order for the therapeutic agent patch 505 to the patient's house.

Referring now to FIGS. 8A through 8F, a discussion will be presented of various waveforms 800 or current output variations (over time) and their characteristics which can be used to promote delivery or retention of one or more therapeutic agents 51. Embodiments of these waveforms can be used for embodiments of the invention having a single or two or more active electrodes 20. Numerous embodiments described herein provide for waveforms 800 that vary between a given polarity and zero, wherein at that polarity, the current (e.g., current 310) causes the therapeutic agent 51 to be repelled into the skin. In other embodiments, the waveforms 800 alternate between positive and negative polarity such waveforms are referred to herein as waveforms 801.

For embodiments having a waveform 801 alternating between a positive and negative polarity, the waveform 801 can be a charged balanced wave form 802 configured such that the current delivered to each electrode assembly (e.g., assemblies 20 and 30) in use is a charged balanced AC current. A charged balance AC current means over a given duration, the amount of current delivered to the skin at each polarity is substantially equivalent. As used herein substantially equivalent means that two values are within 80% of one another, and more preferably within 90% or 99% over the period of one or more waveforms. By orienting the waveform to alternate in a charged-balance fashion, electrical toxicity or other damage to the skin can be reduced or minimized. In other embodiments, an alternating current waveform is used that is oriented towards being balanced in charge, but some asymmetry may exist.

Embodiments of waveforms 800 described below are variable between a minimum and maximum value. Some embodiments of waveform 800, such as described with FIG. 8b , may alternate in charge value (i.e. include reverse polarity) such waveforms are referred to herein as alternating charge waveforms 801. In such embodiments, the current delivery may be balanced in charge so that waveform 801 is a charged balanced waveform 802 as described above.

FIG. 8a illustrates a waveform 800 that includes an extended or long drug delivery period or duration 840 (which may correspond to delivery period 340 shown in FIG. 5c ), according to an embodiment. In some embodiments, the skin may be assumed to handle only a maximum amount of current in a given duration (maximum current delivery) (e.g. 80 milliamps per minute). For a given amperage, the duration of the output of an alternating power source (e.g., power source 100 described above) may be set so as to not exceed the maximum current delivery. The delivery duration 840 may be set to some portion or fraction (e.g. 50% for n=2) of the overall period of the current output I₁. For example, in some implementations, the maximum current delivery (I₁) is assumed to be 80 milliamps for one minute. In such an implementation, the delivery duration is set for 20 seconds on 4 milliamp output. Rather than switch to negative polarity, the output of the power source 100 may alternate to no amperage output (rather than switch polarity). While the waveform 800 depicted in FIG. 8A is rectangular, various embodiments of waveforms 800 may have alternative shapes (e.g. sinusoidal, trapezoidal), with the current delivery corresponding to the area under the curve. In the example shown by FIG. 8A, an alternating power source 100 initiates a delivery duration 840 on one electrode (e.g., active electrode 20), with delivery durations being set by a current that has a polarity that matches that of the charge of the therapeutic agent. The current may alternate to zero output, in which the drug delivery is substantially ceased. Thus, the non-delivery duration 830 may coincide with no current output, rather than reverse current. In other embodiments, non-delivery duration 830 is achieved through the use of a current which has a polarity which is opposite to the charge of active agent 51 as described below in the embodiment of FIG. 8b and above in the embodiment of FIG. 5b (e.g., in the form of holding current 320).

FIG. 8B illustrates another embodiment in which the alternating power signal outputs a symmetrical wave 803 such as symmetrical square wave 804. FIG. 8B (and other waveforms illustrated herein) illustrates use of charge balanced waveforms 802 to deliver charge balanced alternating currents. For example, symmetrical waveforms in polarity may be considered as charged balanced. Depending on the application, the period P of the cycle of waveform 802 may be long (e.g. 20 minutes) or short ( 1/60 seconds). The delivery duration 840 may correspond to half of the period P of the waveform 802. In the implementation shown, a reverse current is used in the non-delivery duration 830, to actively prevent agent delivery to the skin.

FIG. 8C illustrates another embodiment of the invention in which the alternating power signal outputs an asymmetrical wave 805 such as an asymmetrical square wave 806, in that the delivery duration 840 is different than the non-delivery duration 830. More specifically, the asymmetrical square wave 805 may include longer delivery durations (t₁), followed by short(er) rest durations (t₂). The rest durations may correspond to periods of no current, or as shown, reverse current (I₂). In one application, the rest duration enables the skin layer to recuperate from the drug delivery in the prior duration (e.g., to dissipate any heat, concentration of ions, or other by products resulting from the delivery of current). As an alternative or variation, the rest period may follow a period where no current is applied to the skin layer, so as to enable the skin layer to recuperate from application of current.

FIG. 8D illustrates another embodiment in which the alternating power signal has a trapezoidal waveform 807, so as to include ramp-up and/or ramp-down periods 808 and 809. As depicted, I₁ is the maximum current output generated from an alternating power source (e.g. power source 100). The ramp-up period 808 extends for a duration t_(r), that is selected for reasons that include enabling the user to physically accustom to the application of current and/or delivery of therapeutic agent 51. The ramp-up period 808 may be long, to enable the ramp-up duration to be effective. In an embodiment, a ramp-down period 809 may optionally be implemented.

FIG. 8E and FIG. 8F illustrate alternative waveform variations including compound waveforms 813 in which high-frequency oscillations 811 are superimposed on a low frequency base waveform 810. The base waveform 810 may have a period P₈₁₀ that lasts seconds or minutes, corresponding to output current to the electrode assemblies ranging from a maximum (e.g., 4 mA) to no current and/or reverse current. The high-frequency oscillations reflect small variations in the current value at instances in the period. The period P₈₁₁ of the high-frequency oscillations 811 may be one or more magnitudes shorter than that of the base waveform. As an example, the base waveform 800 may have a period P₈₁₀ ranging from seconds to minutes, and the high-frequency oscillations of the waveform may have a period that ranges between milliseconds and seconds. The effect of the high-frequency oscillations 811 is to reduce the effects of the capacitive charge in the skin layer in receiving the therapeutic agent 51. The high frequency oscillations 811 may also be used to facilitate transport of the therapeutic agent through the skin including the stratum corneum by causing oscillations in the movement of the therapeutic agent as it travels through the skin so as to find pathways of least resistance through the skin. In such embodiments, the high frequency oscillations may be adjusted to enhance this effect through use of modeling (e.g., pharmacokinetic modeling) and/or the patient's age, skin type and skin location

The base waveform 810 may be selected for considerations such as described in prior embodiments. For example, in FIG. 8E, the waveform 813 includes a ramp-up time period 808. In FIG. 8F, the waveform 800 has a delivery duration 840 that is switched to a non-delivery duration 830. An embodiment of FIG. 8F illustrates that the high-frequency oscillations 811 may be generated to be present only during the delivery duration 840.

Fentanyl Applications

A discussion will now be presented on fentanyl and the use of various embodiments of the invention for its transdermal delivery. Such embodiments can include various systems, patch and electrode assemblies described herein. The forms of fentanyl which may be delivered by various embodiments of the invention include, without limitation, fentanyl and its analogues and derivatives as well as salts of fentanyl such as fentanyl hydrochloride, fentanyl citrate and fentanyl pamoate. Fentanyl (also known as fentanil) is a potent synthetic narcotic analgesic with a rapid onset and short duration of action. It is a strong agonist at the μ-opioid receptors. It is manufactured under the trade names of SUBLIMAZE, ACTIQ, DUROGESIC, DURAGESIC, FENTORA, ONSOLIS INSTANYL, ABSTRAL and others. Historically, it has been used to treat chronic breakthrough pain and is commonly used before procedures as an anesthetic in combination with a benzodiazepine. Fentanyl is approximately 100 times more potent than morphine with 100 micrograms of fentanyl approximately equivalent to 10 mg of morphine and 75 mg of pethidine (meperidine) in analgesic activity. Typically, the fentanyl delivered by various embodiments of the invention (including its analogues or derivatives) will comprise an aqueous solution of a water soluble fentanyl salt. In some embodiments, the aqueous solution is contained within a hydrophilic polymer matrix such as a hydrogel matrix. The hydrogel matrix may be contained in reservoir 21, tissue contacting layer 24 or other portion of an electrode/patch assembly such as assemblies 14 and 15 cp described herein. The fentanyl (or analogue or derivative) salt-containing hydrogel can suitably be made of any number of materials including a hydrophilic polymeric material, such as one that is polar in nature so as to enhance the drug stability. Suitable polar polymers for the hydrogel matrix comprise a variety of synthetic and naturally occurring polymeric materials. In one embodiment, the hydrogel formulation comprises a suitable hydrophilic polymer, a buffer, a humectant, a thickener, water and a water soluble fentanyl or analogue or derivative salt. The suitable hydrophilic polymer may comprise a hydrophilic polymer matrix which in one or more embodiments may correspond to polyvinyl alcohol such as a washed and fully hydrolyzed polyvinyl alcohol (PVOH). A suitable buffer includes an ion exchange resin which is a copolymer of methacrylic acid and divinylbenzene in both an acid and salt form. One example of such a buffer is a mixture of Polacrilin (the copolymer of methacrylic acid and divinyl benzene available from Rohm & Haas, Philadelphia, Pa.) and the potassium salt thereof. A mixture of the acid and potassium salt forms of Polacrilin functions as a polymeric buffer to adjust the pH of the hydrogel to about pH 6. Use of a humectant in the hydrogel formulation is beneficial to inhibit the loss of moisture from the hydrogel. An example of a suitable humectant is guar gum. Thickeners are also beneficial in a hydrogel formulation. For example, a polyvinyl alcohol thickener such as hydroxypropyl methylcellulose aids in modifying the rheology of a hot polymer solution as it is dispensed into a mold or cavity. The hydroxypropyl methylcellulose increases in viscosity on cooling and significantly reduces the propensity of a cooled polymer solution to overfill the mold or cavity. In one embodiment, the fentanyl (or analogue or derivative) salt-containing hydrogel formulation comprises about 10 to 15 wt % polyvinyl alcohol, 0.1 to 0.4 wt % resin buffer, and about 1 to 2 wt % fentanyl (or analogue or derivative) salt. The remainder is water and ingredients such as humectants, thickeners, etc. Suitable doses of fentanyl for administration over a delivery period include, for example, 20 to 60 micrograms, or 35 to 45 micrograms, or 40 micrograms. A delivery period typically is up to, for example, 20 minutes. Generally 10 to 100 doses of fentanyl are delivered over a 24 hour period in order to achieve the desired analgesic effect; for example, 40, 60 or 80 doses of fentanyl can be delivered over a 24 hour period. Consequently, the total dose of fentanyl delivered for a 24 hour period will generally range from 0.2 to 6.0 milligrams, or 0.35 to 4.5 milligrams, or 0.4 to 4.0 milligrams, or 3.0 milligrams.

Suitable analogues of fentanyl include, without limitation, the following: alfentanil (trade name ALFENTA), an ultra-short-acting (five to ten minutes) analgesic; sufentanil (trade name SUFENTA), a potent analgesic for use in specific surgeries and surgery in heavily opioid-tolerant/opioid-dependent patients; remifentanil (trade name ULTIVA), currently the shortest-acting opioid, has the benefit of rapid offset, even after prolonged infusions; carfentanil (trade name WILDNIL) an analogue of fentanyl with an analgesic potency 10,000 times that of morphine and is used in veterinary practice to immobilize certain large animals such as elephants; and lofentanil an analogue of fentanyl with a potency slightly greater than carfentanil. Doses of fentanyl analogues are selected taking into consideration their individual potency and pharmacokinetics. For example, for a typical delivery period of up to 20 minutes, suitable doses of sufentanyl include, for example, 2.3 to 7 micrograms, or 4 to 5.5 micrograms, or 4.7 micrograms. In various embodiments, 10 to 100 doses of sufentanyl are delivered over a 24 hour period in order to achieve the desired analgesic effect; for example, 24, 30, 40, 60 or 80 doses of sufentanyl can be delivered over a 24 hour period. Consequently, the total dose of sufentanyl delivered for a 24 hour period can range from 23 to 700 micrograms, or 40 to 550 micrograms, or 47 to 470 micrograms.

Examples

Various embodiments of the invention are further illustrated with reference to the appended example which details the use of embodiments of a biphasic transdermal iontophoreritic delivery system. Portions of the example are also described in a paper entitled: Biphasic Transdermal Iontophoretic Drug Delivery Platform (McLaughlin, G. W, et al Conf. Proc. IEEE Eng. Med. Biol. Soc. 2011 August; 2011:1225-8) which is incorporated by reference herein for all purposes. It should be appreciated that this example is presented for purposes of illustration and the invention is not to be limited to the information or the details therein. For example, while the example presented describes the delivery of ferrous chloride, it should be understood that various embodiments of the invention can be used for the delivery of any number of compounds using this approach including, for example, various opioids and other analgesics (e.g., fentanyl), anitemetics, (e.g., Dimenhydrinate) and other therapeutic agents.

Methodology

System Description:

One embodiment of a system that was tested for delivery of therapeutic agent comprised an active electrode, passive electrode, iontophoresis system and a programmer which are described below.

Active Electrode:

This was constructed by using a DuPel Model #198809-001 (Empi, Inc., Clear Lake, S. Dak., USA) electrode with the buffering agent removed and replaced with a teabag filled with two sheets of 3M gauze with 4.0 ml of solution. The solution was prepared by dissolving 1.2 g of FeCl2 (Sigma-Aldrich, St. Louis, Mo., USA) and 300 mg of Poly-Ethylene Oxide (PEO, Mol wt. 100 k) into 4 ml of DI water. The active electrode area was 13.3 cm2.

Passive Electrode:

This was constructed using a DuPel Model#198809-001 electrode with the buffering agent removed and replaced with a teabag filled with two sheets of 3M gauze and 300 mg of Polyethylene Oxide (PEO) with 4 ml of DI water added. The active electrode area was 13.3 cm2.

Iontophoresis System:

This comprised a custom made unit that was controlled by a MSP430F428 (Texas Instruments, Dallas, Tx, USA) microcontroller. This microcontroller coordinated the activities between the switch states of an H-bridge circuit in conjunction with a variable current source. The H-bridge had a programmable voltage rail with a resolution of ˜650 mV steps and a maximum compliance voltage of 80V. The variable current source had a programmable current target with a resolution of ˜40 μxA with an upper limit of 5 mA. The microcontroller was able to update these values at a rate of 5 Hz along with measure and store their values with a time stamp for data archival purposes. Two AA batteries were used to power the system. These batteries were capable of providing up to 40 hours of operation under a standard therapy profile. FIG. 1 shows a picture of the system along with a simplified block diagram of the internals.

Programmer:

This comprised a personal computer that was able to be interfaced to the iontophoresis system via a USB cable. The application code used to program the device was written in TCL/TK. This program was able to set the therapy pulse duration and current value along with the inhibit pulse duration and current value. It was also capable of specifying the total therapy duration. In addition, the programmer was also able to retrieve the data stored in the unit for analysis.

Experimental Setup:

Ten in-vitro test chambers were constructed out of a block PTFE and filled with 120 ml of Hanks Buffered Salt Solution (HBSS). Freshly excised abdominal skin from a male Yorkshire pig (35 kg) was sectioned into 10 (100 mm×175 mm) pieces. Yorkshire pig skin was used as it has been shown to closely mimic the properties of human skin. The subcutaneous fat beneath the dermis layer of the skin was removed so that only the stratum corneum, epidermis, basal layer and dermis layers remained. The skin was then shaved and inspected for blemishes or scratches that might alter transport. Each test chamber had a piece of skin placed on top. Particular care was taken to not damage the integrity of the skin. The skin was affixed to the test chamber via 1¼″ clips. The active and passive electrodes were then placed on the pig skin and attached to the iontophoresis system. All skin irregularities were avoided during this process.

The iontophoresis system was configured to provide a 6 hour therapy session. The first hour of the therapy session consisted of the system in an inhibit mode with a current value of −3 mA. The second hour of the therapy session was a drive mode with a current value of 3 mA. In hour 3 and 4 the system was in the inhibit mode with a current value of −3 mA. In hour 5 the system was in a drive mode with a current value of 3 mA and in hour 6 the system was in an inhibit mode with a current value of −3 mA.

The experimental chambers were placed on magnetic stirrer-hotplates to maintain the HBSS solution between 29° C. to 34° C., which kept the surface of the pig skin between 28° C. to 33° C. Samples of 1 ml were drawn every 15 minutes from the reservoir, using a 25 gauge needle. An equivalent volume of HBBS solution was replenished to maintain the level in the test chamber. During the data analysis, appropriate correction factors were used to compensate for this fluid replacement.

Upon completion of the therapy, the skin samples were visually examined for irritation and or staining. The samples were then photographed. The concentration of iron was quantified, after the required dilutions, by using a standard colorimetric assay. The samples were added to an acidic buffered reagent containing hydroxylamine, thiourea and Ferene (5,5′ (3-(2-pyridyl)-1,2,4-triazine-5,6 diyl)-bis-2-furansulfonic acid, disodium salt). The acidic pH of the buffered reagent was used to release the ferric iron, which is then reduced to ferrous form by the hydroxylamine. This ferrous iron then reacted with the Ferene producing a colored complex. The absorption of this ferrous-Ferene complex was then read at 595 nm using a spectrophotometer (Multiscan EX; Thermo Electron Corporation, Vantaa, Finland). The absorption spectrum provided a proportional relationship to that of the iron concentration within the sample. This assay method provides a lower limit of quantification of 50 μg/dl.

Results

The average of the ten samples was taken for each 15 minute sample period to obtain a mean cumulative density data set. This data set was then used as the measured output of the system to be identified, y(t). The input to the system was the known integral of the active portion of the therapy session, x(t). These sets of data were than used to identify the system transfer function, h_(est)(t) which is shown in block diagram form in FIG. 9.

The transfer function h_(est)(t) of the system was estimated based on Fourier transforms of the input and output signals on the system.

${H(\omega)} = {\frac{\overset{\_}{X(\omega)} \cdot {Y(\omega)}}{{{X(\omega)}}^{2}} = \frac{{\hat{R}}_{xy}}{{\hat{R}}_{xx}}}$

An inverse Fourier transform was then taken of the resulting transfer function. This data set was then cropped, limiting the memory of the system transfer function to a period of 10 samples or 2.5 hours. The known input data was then convolved with this transfer function to obtain the estimated cumulative system density response. This data was then analyzed to determine how well the predicted output matched the measured output. This resulted in an R2 value of 0.912, confirming a good correlation between the model and the data.

Next, the derivative of the measured cumulative density data was taken. In order to obtain an accurate estimate of the derivative of the data a first order least means squares fit was performed for each 4 samples of the data moving in a single sample step. The slope of this fit was then used as the representative value for the derivative of the data. This data was then analyzed using the same method as that of the cumulative density function data. This resulted in an R² value of 0.802, confirming that the predicted model correlated well with the estimated pulsatile drug delivery model as shown in FIGS. 10a and 10 b.

The measured results show a time lag of around 45 minutes between the start of the therapy cycle and the detection of the FeCl₂ in the saline solution. This time lag is expected in the in-vitro studies due to the transport time required to traverse all the layers of the skin and reach the saline bath. In an in-vivo study this lag would be expected to be substantially smaller due to an active micro-capillary system just under the basal layer, alleviating the need for the material to pass through the dermis layer.

CONCLUSION

The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to limit the invention to the precise forms disclosed. Many modifications, variations and refinements will be apparent to practitioners skilled in the art. For example, the iontophoretic patch can be modified in size, shape and dose of therapeutic agent for different medical conditions, different tissue sites as well as for various pediatric applications. Additionally, the patch assemblies, methods and control algorithms can also be modified for skin type, therapeutic agent dose, as well as various pediatric applications.

Elements, characteristics, or acts from one embodiment can be readily recombined or substituted with one or more elements, characteristics or acts from other embodiments to form numerous additional embodiments within the scope of the invention. Moreover, elements that are shown or described as being combined with other elements, can, in various embodiments, exist as standalone elements. Hence, the scope of the present invention is not limited to the specifics of the described embodiments, but is instead limited solely by the appended claims. 

What is claimed is:
 1. A patch assembly for iontophoretic transdermal delivery of a therapeutic agent to a patient, the assembly comprising: a patch for iontophoretic transdermal delivery of the therapeutic agent, the patch having a tissue contacting side, a non-tissue contacting side, a therapeutic agent reservoir and a first and second electrode, at least one of the electrodes electrically coupled to the therapeutic agent reservoir; a current source coupled to the patch and electrically coupled to the first and second electrode; and a controller coupled to the patch for controlling the iontophoretic transdermal delivery of the therapeutic agent; the controller configured to deliver a dose of therapeutic agent from the patch into the skin during a first period using a first current having a polarity and magnitude to repel the therapeutic agent out of the patch; and retain the therapeutic agent in the patch during a second period using a second current having a polarity and magnitude to retain the therapeutic agent in the patch such that delivery of the therapeutic agent into the skin during the second period is minimized, wherein the first period comprises a delivery period and the second period comprises a non-delivery period which together comprise a delivery cycle. 